Bushfires in Australia are frequent events during the hotter months of the year, due to Australia's mostly hot, dry climate. Each year, such fires impact extensive areas. While they can cause property damage and loss of human life, certain native flora in Australia have evolved to rely on bushfires as a means of reproduction, and fire events are an interwoven and an essential part of the ecology of the continent. For thousands of years, Indigenous Australians have used fire to foster grasslands for hunting and to clear tracks through dense bush.

Victoria has seen the majority of the deadliest and largest bushfires in Australia, most notably the 2009 Black Saturday fires, where 173 people were killed, around 2,000 homes and structures were destroyed, towns were gutted, and some, such as Marysville, were destroyed.

Global warming is increasing the frequency and severity of bushfires[1] and will lead to increased days of extreme fire danger.[2]

Bushfires in Australia, are generally defined as any uncontrolled, non-structural fire burning in a grass, scrub, bush, or forested area. Australia, being a geographically and meteorogically diverse continent, experiences many types of bushfires. Fires can be divided into two main categories, depending on topography of the area.

Hilly/mountainous fires – Burn in hilly, mountainous or alpine areas which are usually densely forested. The land is less accessible and not conducive to agriculture, thus many of these densely forested areas have been saved from deforestation and are protected by national, state and other parks. The steep terrain increases the speed and intensity of a firestorm. Where settlements are located in hilly or mountainous areas, bushfires can pose a threat to both life and property.

Flat/grassland fires – Burn along flat plains or areas of small undulation, predominantly covered in grasses or scrubland. These fires can move quickly, fanned by high winds in flat topography, they quickly consume the small amounts of fuel/vegetation available. These fires pose less of a threat to settlements as they rarely reach the same intensity seen in major firestorms as the land is flat, the fires are easier to map and predict and the terrain is more accessible for firefighting personnel. Many regions of predominantly flat terrain in Australia have been almost completely deforested for agriculture, reducing the fuel loads in these areas.

Common causes of bushfires include lightning,[3]arcing from overhead power lines, arson, accidental ignition from agricultural clearing, grinding and welding, campfires, cigarettes and dropped matches, machinery, and controlled burn escapes.

Epicormic shoots sprouting vigorously from epicormic buds beneath the thick bushfire damaged bark of a Eucalyptus tree – one of the strategies evolved by plants to survive bushfires

Bushfire damage to forests in East Gippsland, Victoria from the of 2003, two years after fires swept through the area, showing the recovery of trees and undercroft

The natural fire regime in Australia was altered by the arrival of humans. Fires became more frequent, and fire-loving species—notably eucalypts—greatly expanded their range.[4] It is assumed that a good deal of this change came about as the result of deliberate action by early humans, setting fires to clear undergrowth or drive game.[5]

Plants have evolved a variety of strategies to survive (or even require) bushfires, (possessing epicormic shoots or lignotubers that sprout after a fire, or developing fire-resistant or fire-triggered seeds) or even encourage fire (eucalypts contain flammable oils in the leaves) as a way to eliminate competition from less fire-tolerant species.[6]

In 2009, a standardised Fire Danger Rating (FDR) was adopted by all Australian states. During the fire season the Bureau of Meteorology (BOM) provides fire weather forecasts and by considering the predicted weather including temperature, relative humidity, wind speed and dryness of vegetation, fire agencies determine the appropriate Fire Danger Rating.[8] In 2010, following a national review of the bush fire danger ratings, new trigger points for each rating were introduced for grassland areas in most jurisdictions. See for example the following glossary[9]

Fire Danger Ratings are a feature of weather forecasts and alert the community to the actions they should take in preparation of the day. Ratings are broadcast via newspapers, radio, TV, and the internet.

Note that in Western Australia, where Fire Danger Ratings are based on the Grassland FDI, that Extreme relates to FDI between 75 and 99 and Catastrophic to FDI above 100. Fire agencies may consider other factors in addition to the FDI in determining ratings

In Victoria, the Country Fire Authority (CFA) provides firefighting and other emergency services to country areas and regional townships within the state, as well as large portions of the outer suburban areas and growth corridors of Melbourne not covered by the Metropolitan Fire Brigade.[12] On Crown land, which covers roughly 20 per cent of Victoria, the Department of Environment and Primary Industries is the lead fire agency.

Bushfires in Australia can occur all year-round, though the severity and the "bushfire season" varies by region.[14] These seasons are commonly grouped into years such as "2006-07 Australian bushfire season" and typically run from June one year until May the next year.

In southeast Australia, bushfires tend to be most common and most severe during summer and autumn (December–March), in drought years, and particularly severe in El Niño years. Southeast Australia is fire-prone, and warm and dry conditions intensify the probability of fire.[15] In northern Australia, bushfires usually occur during the dry season (April to September),[16] and fire severity tends to be more associated with seasonal weather patterns. In the southwest, similarly, bushfires occur in the summer dry season and severity is usually related to seasonal growth. Fire frequency in the north is difficult to assess, as the vast majority of fires are caused by human activity, however lightning strikes are as common a cause as human-ignited fires and arson.

Australia's climate has been trending toward more bushfire weather over the last 30 years.[17] The Climate Commission found that "The intensity and seasonality of large bushfires in south-east Australia appears to be changing, with climate change a possible contributing factor."[18] Climate change is increasing the severity and frequency of heatwaves in Southeast Australia and the probability of extreme fire risk. As the fire seasons become longer, there is less time for fuel reduction burns to control the bush fuel load.[2]

A 2006 report by the Bushfire CRC acknowledges the complexity of climate predictions pointing out "Much of [Australia's] vegetation has a complex evolutionary and dependent relationship with fire. Fire has been part of these environments for tens of thousands of years and much native flora and fauna remains dependent on it in various ways."[19] In 2007, a study by the CSIRO (the national government body for scientific research in Australia), found evidence that climate change will lead to increases in very high and extreme fire danger rating days and earlier onset of the fire season.[20] Other studies investigating the historical record identify significant changes in Australia's bushfire season as a result of human activity.[21]

Bushfires have accounted for over 800 deaths in Australia since 1851 and the total accumulated cost is estimated at $1.6 billion.[22] In terms of monetary cost however, they rate behind the damage caused by drought, severe storms, hail, and cyclones,[23] perhaps because they most commonly occur outside highly populated urban areas.

Australia's worst ever recorded natural disaster was a bushfire, the VictorianBlack Saturday Bushfires in 2009, where 173 people lost their lives.

Some of the most severe Australian bushfires, in chronological order, have included:

Fire so intense it created a 12 km-wide convection column, generating its own weather and lightning strikes.

2014 East Gippsland bushfires

Victoria

166,000 ha

15 January to 10 March 2014

0

On 15 January several lightning strikes started fires in forested areas. During February further lightning strikes occurred, and especially on 9 February these fires grew and coalesced into a 166,000ha Goongerrah-Deddick Fire complex (850 km perimeter) with other smaller fires affecting a further 10,000 ha. 11 homes destroyed.

^Milman, Oliver (24 October 2013). "Climate Council finds 'clear link' between bushfires and climate change". The Guardian. Retrieved 26 October 2013."There is a “clear link” between climate change and bushfires, with the current New South Wales fires influenced by a rising frequency of hot, dry days, according to the climate body that had its funding withdrawn by the Coalition government. * * * The Climate Council’s interim findings, drawn from 60 peer-reviewed studies, show climate change is influencing the number of extremely warm days in Australia, as well as prolonged periods of low rainfall."